There has been much research on the development of strong and safe polymer materials for special purposes. However, discarded polymers are now socially recognized as a severe environmental problem all over the world, leading to efforts to develop environmentally-friendly polymer materials as an alternative.
Environmentally-friendly polymers may be primarily classified into photodegradable and biodegradable polymers. Biodegradable polymers typically include a functional group that can be decomposed by microorganisms.
Among these polymers, aliphatic polyester polymer has gained the most attention, since it has excellent working properties and easily adjustable decomposition characteristics. In particular, polylactic acid (PLA) has a world-wide market share of 150,000 tons and expansively covers the field where plastic is commonly used, for example, as food packaging materials and containers, cases for electronics, and the like. Polylactic acid resin has been primarily used for disposable products such as food containers, wraps, films, and the like due to its biodegradable characteristics. Current examples of polylactic acid include those produced by American Natureworks LLC, Japanese Toyota Motor Co., and the like.
However, conventional polylactic acid resin can lack adequate molding property, mechanical strength, and heat resistance, and may be easily destroyed, when fabricated into a thin film. Further, since it has low resistance to high temperatures, molded products made therefrom may also be distorted at 60° C. or higher.
Japanese Patent Laid-Open Publication Nos. 2004-190026, 2006-335909, and 2006-182994 disclose melt mixing polylactic acid, a polycarbonate, and a flame retardant. However, the polycarbonate insufficiently improves the weak mechanical and thermal properties of the polylactic acid.
Japanese Patent Laid-Open Publication No. 2006-111858 discloses a method of mixing a compatibilizer with a polylactic acid resin/polycarbonate resin to improve the appearance of a molded product. However, this publication does not disclose improved mechanical strength and heat resistance.
Japanese Re-laid-Open Patent No. WO06/097979 discloses a polylactic acid/thermoplastic resin including a compatibilizer, but this resin is not flame retardant. In addition, this publication does not clarify how to prepare the cornpatibilizer.